1. Field of the Invention
The present invention relates to a sending radio station, a receiving radio station, a radio communication system, and a radio communication method in a radio communication system (for example, the radio communication system which executes OFDM (Orthogonal Frequency Division Multiplexing) transmission or OFCDM (Orthogonal Frequency Code Division Multiplexing) transmission) with a hierarchical cell structure (so-called cell-in-cell structure) for executing data transmission using orthogonal carrier frequency bands.
2. Related Background Art
In FIG. 1, there is shown a radio sending system using one or more sending radio stations which control a certain range of area 90, and a sending radio station forming a small scale cell 80 which can receive signal from the one or more sending radio stations and has smaller Equivalent Isotropically Radiated Power (EIRP) as compared with the one or more sending radio stations. In addition, in the description of this specification, one or more sending radio stations controlling the certain range 90 will be referred to as a “large cell sending radio station” and the sending radio station having small EIRP as compared with the large cell sending radio station and forming the small scale cell 80 will be referred to as a “small cell sending radio station”. Moreover, as shown in FIG. 1, it is assumed that the large cell sending radio station uses a frequency band f1, and the small cell sending radio station uses a frequency band f2.
In FIG. 2, a functional block configuration of a conventional sending radio station 1 having small EIRP and a conventional receiving radio station 11 is shown. As shown in this FIG. 2, in the receiving radio station 11, in order to receive data sent from each sending base station in the receiving radio station 11, it was necessary that after the data having been separated by a filter 12 which passes only the frequency band f1 and stops the frequency band f2, and a filter 13 which passes only the frequency band f2 and stops the frequency band f1, respectively, a desired frequency band is selected out of the separated frequency bands by a switcher 14 and inputted to a receiving section 15. This is because the signal of the frequency band not supposed to be received will cause no deterioration of the reception quality due to interferences at the time of the demodulation.
On the other hand, techniques involving a method of symbol synchronization have been proposed in the prior art, and, for example, a technique involving the method of symbol synchronization in the relay station of the broadcast field has been disclosed in Japanese patent laid-open gazette, Heisei 7-283806.